The visual function is a complex sensory function by the optical system, the nervous system and the brain. The optical system includes the cornea, the crystalline lens, the pupil (iris), and the like, and performs adjustment of light amount, focus adjustment, and the like. The nervous system includes the retina, the visual pathways, and the like. Photoreceptor cells are arrayed in the retina. The photoreceptor cells convert an image formed by the optical system on the retina (light intensity, wavelength distribution, and the like) into nervous signals. The nervous signals are transmitted to the brain through visual pathways, and processed by the brain.
Visual field examination (or perimetry) is a typical example of the visual function examination. The visual field examination includes static visual field examination and dynamic visual field examination. In the static visual field examination, a photic stimulus (spot light, etc.) whose size is constant and whose intensity (brightness) is variable is projected to a specific position on the retina. The examinee pushes a button when having visually recognized the photic stimulus. Through sequential performance of this process for a plurality of positions of the retina, sensitivity for each site of the retina (that is, sensitivity distribution) can be obtained. In the dynamic visual field examination, the projection position of a photic stimulus onto the retina is moved. The examinee pushes a button when having visually recognized the photic stimulus. Thereby, a range visible by the subject's eye (that is, a shape of the visual field of the subject's eye) is obtained.
Another typical examination is flicker perimetry. In the flicker perimetry, a photic stimulus whose flicker frequency (frequency of brightness change) is variable is presented to the subject's eye, and a threshold value of the flicker frequency recognizable by the subject is obtained.
Patent Document 1: Japanese Unexamined Patent Publication No. 2014-36844
Patent Document 2: Japanese Unexamined Patent Publication No. 11-267101
As described above, the visual function examination is performed based on the subject's responses to photic stimuli. Therefore, when the subject is unfamiliar with the examination or is an elderly person, the subject may make mistakes with his/her response or he/she may provide a delayed response, leading to problems such as decreasing reliability of the examination and prolongation of the examination. Considering that the time required for a visual function examination is relatively long in general (for example, about several tens of minutes), prolongation of the examination reduces the concentration of the subjects and causes a further decrease in reliability of the examination as well as is putting the examiner under a great deal of strain.